盲源分离与波束形成融合抑制方向性强干扰研究

针对强干扰严重影响线列阵声纳弱目标检测的问题,融合盲源分离（Blind source separation,BSS）与波束形成提出了一种抑制方向性强干扰的方法.首先在干扰方位形成波束得到干扰信号估计,然后对阵列接收信号的每个子带采用盲源分离方法得到分离信号和解混矩阵估计,并通过对分离信号和干扰信号进行子带谱相关抑制干扰,再将抑制干扰后的分离信号重构回阵元域信号,最后采用波束形成方法完成目标方位估计.利用模拟器数据和海试数据对方法进行了验证,结果表明,该方法能有效地抑制方向性强干扰,明显提高了弱目标信号的空间谱能量,增强了声纳检测弱目标的能力.     

被动合成孔径远程方位估计技术研究

针对水下自动航行器(AUV)物理孔径有限以及目标远程探测的需求,提出了改进的波束域被动合成孔径处理算法BDPSA。对水下航行器物理线列阵相继时刻测量的波束输出在相位补偿后进行同相叠加,不仅实现了波束输出能量峰值与期望目标方位的对应,而且合成出比AUV物理孔径大得多的有效孔径,从而突破了阵列孔径的限制,获得了比物理孔径高得多的方位分辨力和阵增益。通过对1、1/2、1/3和1/4波束宽度内双目标检测概率和分辨概率的仿真研究,结果表明:同现有的高分辩方位估计算法MUSIC和MVDR相比,BDPSA算法具有更低的目标分辨信噪比门限,不仅提高了低信噪比下的检测概率和分辨概率的性能,而且可以实现远距离目标高分辨方位估计,具有一定的应用前景。     

基于平滑相干变换处理的分裂孔径波束形成方法

传统声呐系统通常将全阵波束形成结果直接送显输出,且全阵波束处理往往未有效利用信号的相关性,针对此特点,本文结合平滑相干变换(SmoothedCoherenceTransform,SCOT)处理原理,提出一种基于SCOT预白化处理的分裂孔径波束形成处理方法。该方法首先将阵列孔径一分为二,其次对两子孔径波束输出进行SCOT、互谱处理,最后获得最终的波束输出。与常规全阵波束处理方法相比,本文所提出的方法能有效抑制高噪声频率成分,同时提高目标的方位分辨能力。仿真结果表明,该方法能有效改善波束的输出效果。     

声传感器阵列的实验研究

海洋中对目标的判决主要依靠于水听器阵列对水声信号的检测。为了对比声压阵与矢量阵对信号的检测能力,首先计算机仿真了声压阵和矢量阵的增益及其对目标方位的估计,而后加以实验验证。实验结果表明,矢量阵的增益高于声压阵,且其克服了声压阵左、右舷模糊的问题,能精确的对目标方位进行估计并完成对水下运动目标的航迹跟踪,从而验证了矢量阵的优越性。     

基于多参考信号ICA的目标语音提取方法

为了能够在强噪声、干扰声等复杂环境下提取干净的目标语音,提高输出信号的信噪比和信干比,本文提出了一种基于多参考信号ICA算法的语音提取方案。该方法利用声源定位、波束形成和小波分解等算法结果作为参考信号,应用基于负熵的FastICA算法估计目标语音。使用麦克风阵实测语音信号的仿真实验证明,本文提出的算法能有效地抑制背景噪声和干扰声,恢复目标语音波形和语谱图。与常规波束形成和ICA算法相比较,本文的处理方法有更好的性能,输出信号的信噪比和信干比更高。     

水下运动阵列多目标检测和方位估计一体化方法

水下多目标的远程检测和方位估计是是水下阵列信号处理的两个关键问题。传统的方法是将这两个方面分开处理,先通过某种检测方法来检测目标个数,然后再利用某种方位估计方法来确定各个目标的方位。这样前面目标检测的结果的好坏就直接影响到后面目标方位估计的性能。针对低信噪比下传统检测方法的性能差且不能同时给出方位估计的问题,提出了一种基于水下运动阵列合成孔径技术的多目标检测和方位估计一体化新方法SATDE。该方法充分利用水下运动阵列合成孔径技术来提高阵增益和角度分辨率,并利用体现信号能量的MVDR空间谱函数来确定目标的个数及方位。仿真结果表明,对于相干信号来说,提出的方法在低信噪比下的检测性能显著优于AIC和MDL等传统方法,并且可以同时给出正确的方位估计。     

基于改进的AR模型的逆波束形成方法研究

逆波束形成是利用各阵元接收信号间的互功率谱估计声场平面波强度的理论,较之常规波束形成,它具有更高的方位分辨能力和噪声干扰抑制能力。在分析逆波束形成理论及其傅立叶类求解算法的基础上,提出了基于改进的AR模型的求解方法。该方法将参数模型引入到逆波束形成的求解当中,通过引入前向后向平均,克服了信号协方差矩阵在小信噪比和快拍数较少情况下估计不准的问题,从而减轻了旁瓣的起伏,有助于实现对弱目标信号的检测与估计。通过大量计算机仿真实验,证实了所提算法的可行性和优越性。     

波束域ETAM算法在无人水下航行器中的应用

线列阵的方位分辨率受阵列孔径所限制;结合基于UUV(Unmanned Undersea Vehicle)小型拖线阵的应用,针对时域ETAM方法在等强度多源检测时性能下降的问题,提出采用波束域ETAM方法进行被动孔径合成处理;在满足时空相关特性前提下,该方法利用目标噪声中的低频线谱成分,根据时间处理增益转换为空间处理增益思想,通过时间补偿,对阵列孔径进行扩展,从而达到获得高动态空间增益、显著改善目标方位分辨力的目的;分析结果表明,该算法具有很好的多源检测性能,而且进一步验证了其高分辨特性,在UUV平台上具有很高的应用价值.     

基于静态波束综合的波束域预处理算法

针对自适应波束形成的波束域方法在波束覆盖区域外存在强相关干扰源时多目标方位估计失效的问题,提出采用静态波束综合的波束域预处理算法。该算法利用多波束系统输出确定干扰大致方位,再以常规波束的权矢量为期望权矢量,通过求解最优化问题得到最优权矢量,在波束覆盖区域外的相关干扰源附近方位形成较宽零陷。仿真结果表明,该算法在相关和非相关干扰源情况下,均能较好的抑制干扰,进一步提高了波束域预处理方法的抗干扰能力。     

基于单矢量传感器的强干扰噪声抑制方法

通过对单矢量传感器各通道输出不同形式的组合可以抑制干扰噪声,但高次乘方和最小均方误差准则2种方法包含非线性运算,使目标信号产生失真;常用的线性运算方法只能完全抑制与目标方位相差一固定值的干扰信号。对单矢量传感器各通道授予不同的权重系数并进行线性运算,根据最小噪声功率输出准则,在不降低目标信号信噪比的同时,通过调节权重系数,可抑制各向同性噪声场中任一方位的强干扰信号。仿真显示:本方法可在不降低目标信号信噪比和保证目标信号不失真的前提下,完全抑制与目标方位相差70°～290°范围内任一方位的强干扰噪声。     

Only connect: teaching, technology and telesis

Abstract This paper describes an approach to the design of interactive multimedia materials being developed in a European Community project. The developmental process is seen as a dialogue between technologists and teachers. This dialogue is often problematic because of the differences in training, experience and culture between them. Conditions needed for fruitful dialogue are described and the generic model for learning design used in the project is explained.     

European Community policy and the market

Abstract This paper starts with some reflections on the policy considerations and priorities which are shaping European Commission (EC) research programmes. Then it attempts to position the current projects which seek to capitalise on information and communications technologies for learning in relation to these priorities and the apparent realities of the marketplace. It concludes that while there are grounds to be optimistic about the contribution EC programmes can make to the efficiency and standard of education and training, they are still too technology driven.     

一种自适应子融合集成多分类器方法

融合集成方法已经广泛应用在模式识别领域,然而一些基分类器实时性能稳定性较差,导致多分类器融合性能差,针对上述问题本文提出了一种新的基于多分类器的子融合集成分类器系统。该方法考虑在度量层融合层次之上通过对各类基多分类器进行动态选择,票数最多的类别作为融合系统中对特征向量识别的类别,构成一种新的自适应子融合集成分类器方法。实验表明,该方法比传统的分类器以及分类融合方法识别准确率明显更高,具有更好的鲁棒性。     

Avoiding semantic and temporal gaps in developing software intensive systems

Development of software intensive systems (systems) in practice involves a series of self-contained phases for the lifecycle of a system. Semantic and temporal gaps, which occur among phases and among developer disciplines within and across phases, hinder the ongoing development of a system because of the interdependencies among phases and among disciplines. Such gaps are magnified among systems that are developed at different times by different development teams, which may limit reuse of artifacts of systems development and interoperability among the systems. This article discusses such gaps and a systems development process for avoiding them.     

Designing economic np control charts: A programmed simulation approach

This paper presents control charts models and the necessary simulation software for the location of economic values of the control parameters. The simulation program is written in FORTRAN, requires only 10K of main storage, and can run on most mini and micro computers. Two models are presented - one describes the process when it is operating at full capacity and the other when the process is operating under capacity. The models allow the product quality to deteriorate to a further level before an existing out-of-control state is detected, and they can also be used in situations where no prior knowledge exists of the out-of-control causes and the resulting proportion defectives.     

The development of robot art

Going through a few examples of robot artists who are recognized worldwide, we try to analyze the deepest meaning of what is called “robot art” and the related art field definition. We also try to highlight its well-marked borders, such as kinetic sculptures, kinetic art, cyber art, and cyberpunk. A brief excursion into the importance of the context, the message, and its semiotics is also provided, case by case, together with a few hints on the history of this discipline in the light of an artistic perspective. Therefore, the aim of this article is to try to summarize the main characteristics that might classify robot art as a unique and innovative discipline, and to track down some of the principles by which a robotic artifact can or cannot be considered an art piece in terms of social, cultural, and strictly artistic interest. This work was presented in part at the 13th International Symposium on Artificial Life and Robotics, Oita, Japan, January 31–February 2, 2008     

Explanation and prediction: an architecture for default and abductive reasoning

Although there are many arguments that logic is an appropriate tool for artificial intelligence, there has been a perceived problem with the monotonicity of classical logic. This paper elaborates on the idea that reasoning should be viewed as theory formation where logic tells us the consequences of our assumptions. The two activities of predicting what is expected to be true and explaining observations are considered in a simple theory formation framework. Properties of each activity are discussed, along with a number of proposals as to what should be predicted or accepted as reasonable explanations. An architecture is proposed to combine explanation and prediction into one coherent framework. Algorithms used to implement the system as well as examples from a running implementation are given.     

Three Process Perspectives: Organizations, Teams, and People

This paper provides the author's personal views and perspectives on software process improvement. Starting with his first work on technology assessment in IBM over 20 years ago, Watts Humphrey describes the process improvement work he has been directly involved in. This includes the development of the early process assessment methods, the original design of the CMM, and the introduction of the Personal Software Process (PSP)^SM and Team Software Process (TSP){^SM}. In addition to describing the original motivation for this work, the author also reviews many of the problems he and his associates encountered and why they solved them the way they did. He also comments on the outstanding issues and likely directions for future work. Finally, this work has built on the experiences and contributions of many people. Mr. Humphrey only describes work that he was personally involved in and he names many of the key contributors. However, so many people have been involved in this work that a full list of the important participants would be impractical.     

基于复小波噪声方差显著修正的SAR图像去噪

提出了一种基于复小波域统计建模与噪声方差估计显著性修正相结合的合成孔径雷达(Synthetic Aperture Radar,SAR)图像斑点噪声滤波方法。该方法首先通过对数变换将乘性噪声模型转化为加性噪声模型,然后对变换后的图像进行双树复小波变换(Dualtree Complex Wavelet Transform,DCWT),并对复数小波系数的统计分布进行建模。在此先验分布的基础上,通过运用贝叶斯估计方法从含噪系数中恢复原始系数,达到滤除噪声的目的。实验结果表明该方法在去除噪声的同时保留了图像的细节信息,取得了很好的降噪效果。     

How do children do mathematics with LOGO?

Abstract  This paper considers some results of a study designed to investigate the kinds of mathematical activity undertaken by children (aged between 8 and 11) as they learned to program in LOGO. A model of learning modes is proposed, which attempts to describe the ways in which children used and acquired understanding of the programming/mathematical concepts involved. The remainder of the paper is concerned with discussing the validity and limitations of the model, and its implications for further research and curriculum development.